1. Introduction
This invention relates to novel novolak resins and a novel process for making the same. The novel novolak resins are formed from bishydroxymethylated phenols reacted with other reactive phenolics to produce an alternating copolymer. Further reaction of the alternating copolymer, with different reactive phenols or mixtures of reactive phenols, in the presence of an aldehyde leads to the formation of a block copolymer. The copolymer resins may be used alone or in blends with the same or other novolak resins.
2. Discussion of Related Art
The formation of novolak resins by condensation of a phenol with an aldehyde is well known in the art. Toukhy et al in U.S. Pat. Nos. 4,377,631 and 4,587,196 disclose novolak resins produced by condensing with formaldehyde a mixture of m-cresol and p-cresol or o-, m- and p-cresol, with the various cresol isomers present by weight in selected proportions. The average molecular weight of the resins formed is a function of the number of cresol units that become linked by methylene bridges as a result of the reaction with formaldehyde to form the resin molecules. The resin molecules formed are random in nature. The patent teaches that a higher molecular weight novolak may be obtained by increasing the ratio of formaldehyde to cresol thereby increasing the degree of linkage of the cresol units. The patent teaches that the maximum molar ratio of formaldehyde to cresols is 0.9:1. Higher molar ratios of formaldehyde with cresols leads to crosslinking and resin intractability, thereby limiting the extent to which the molecular weight can be controlled.
EPO Application No. 0 118 291, U.S. Pat. No. 4,830,413 discloses novolak resins obtained by the addition condensation of a phenol and formaldehyde wherein the phenol is one in which the average carbon number in any substituent per phenol nucleus is 0.5 to 1.5 and less than 50 mol % of the molecules have substituents at the ortho- or para-position with respect to the hydroxyl group. If these specific conditions for selection of the phenol are not met, the resulting novolak will have slow dissolution rates and will not have the expected improvement in optical properties.
U.S. Pat. No. 4,614,826 describes polynuclear polyhydric phenols prepared by reacting a dihydric phenol with a specific substituted phenol in the presence of an acid catalyst. The dihydric phenols used are catechol, resorcinol and hydroquinone. The substituted phenols used in the reaction are typically the bishydroxyalkyl phenols. The dihydric phenol is ordinarily used in an amount of 1 to 8 moles per mole of the substituted phenol. The resulting polynuclear polyhydric phenols, which contain up to 10 polymer units, are low molecular weight resins. The resins are used to form polyepoxy compounds useful in resins.
U.S. Pat. No. 4,837,121 describes phenolic resins made by reacting a halogen-substituted resorcinol with a para-lower alkyl-substituted 2,6-bis(hydroxymethyl)-phenol compound in the presence of an acid catalyst The mole ratio of the resorcinol compound to the bishydroxymethylphenol used in the condensation reaction ranges from 0.5:1 to 1.7:1. Because of the position of the substituent on the phenolic rings, the condensation polymerization results in ortho-, ortho-bonding between each phenolic structure. The patent further describes the addition of third phenolic compound (m- or p- alkoxy substituted phenol) which will condense with the bishydroxymethyl phenol. However, with the third phenolic compound, only the para-alkoxy substituted phenol gives ortho-, ortho- bonding , while the meta-alkoxy substituted phenol gives a mixture of ortho-, ortho-bonding and ortho-, para- bonding. The resulting resins have molecular weights form about 500 to 10,000. When resins containing the third phenolic compound are desired, they usually comprise about 20 to 60 percent of the phenol feed.